The invention relates to a load adjustment apparatus for a final control element which determines the power of an internal combustion engine, is designed, in particular, as a throttle valve and is arranged on an actuating shaft, in which arrangement the actuating shaft can be driven so as to be pivotable between a minimum-load position and a full-load position by way of an actuating part, connected to it in a rotationally fixed position, by means of a reversible actuating gear, having a preloaded return spring which is designed as a torsion spring and acts on the actuating shaft in the minimum-load direction, and having an emergency-running spring by means of which the actuating shaft can be moved in the full-load direction as far as an emergency-running position.
Load adjustment apparatuses of the type mentioned above are well known under the name E-Gas and are used to adjust power of the internal combustion engine of motor vehicles. To minimize fuel consumption, the minimum-load position in these apparatuses is designed in such a way that, in it, the internal combustion engine only just continues to run smoothly at idling speed. As a result, it is not possible in the minimum-load position to produce sufficient torque to move the motor vehicle. However, this may be necessary if there is a need to drive the motor vehicle out of a danger zone but the load adjustment apparatus can no longer be adjusted by actuating the accelerator pedal owing to failure of the control electronics or of the actuating gear. In the known load adjustment apparatuses, therefore, there is, in addition to the return spring, an emergency-running spring which ensures that if the control electronics or the actuating gear fails the final control element necessarily moves out of the minimum-load position into an emergency-running position, in which the internal combustion engine produces a sufficiently high torque to move the motor vehicle at low speed. This emergency-running position is defined by a stop which can be displaced against the force of the return spring, against which the actuating part is loaded by means of the emergency-running spring and which can be displaced against the force of the return spring by the actuating part when the actuating part moves out of the emergency-running position in the direction of the full-load position.
Apart from the costs involved, the emergency-running spring required to obtain the emergency-running position requires a corresponding installation space and leads to an increase in weight in comparison with a load adjustment apparatus without enforced movement into an emergency-running position in the event of a defect.
The problem underlying the invention is to provide a load adjustment apparatus of the type stated at the outset in such a way that it is as compact as possible in construction and can be produced at reasonable cost.
According to the invention, this problem is solved wherein the return spring and the emergency-running spring are formed by a single torsion spring, the first end of which is connected to the actuating shaft and the other end of which can be moved against the force of the torsion spring between the emergency-running position and the minimum-load position by means of a minimum-load gear coupled to the actuating gear.
By this formation, the single torsion spring is used both as a return spring and as an emergency-running spring and, depending on the actuating angle of the actuating shaft, is stressed either directly by way of the actuating gear or the minimum-load gear coupled to the actuating gear. The actuating shaft thus pivots automatically into the emergency-running position from any position when there are no forces acting on the actuating gear. The elimination of one of the springs makes the load adjustment apparatus according to the invention particularly compact in design and it can therefore be produced at very reasonable cost. Apart from the actuating gear, the only other thing that the load adjustment apparatus according to the invention requires is a minimum-load gear of particularly simple construction.
The preloading of the torsion spring by the minimum-load gear could, for example, be accomplished by securing the second end of the torsion spring on a holding part which is adjustable by the minimum-load gear. However, according to an advantageous development of the invention, the preloading of the torsion spring by the minimum-load gear requires a particularly low level of expenditure in terms of construction if between the emergency-running position and the full-load position, the second end of the torsion spring rests against a stop and, between the emergency-running position and the minimum-load position, can be moved away from the stop.
According to another advantageous development of the invention, the actuating gear can be arranged in a space-saving manner in the load adjustment apparatus if the actuating part has a segment gear designed to mesh with a gearwheel of the actuating gear.
According to another advantageous development of the invention, the actuating gear has a particularly small overall height if the actuating gear has a large-diameter intermediate gearwheel which is driven by a drive pinion and is connected coaxially and in a rotationally fixed position to a small-diameter gearwheel which pivots the actuating part. This configuration furthermore has the advantage that the actuating shaft is pivoted by the actuating gear if the torsion spring breaks. A defect in a single component of the load adjustment apparatus according to the therefore does not lead to complete failure of the internal combustion engine controlled by it.
According to another advantageous development of the invention, the minimum-load gear requires a particularly low level of expenditure in terms of construction if a dog for moving the second end of the torsion spring is arranged on the intermediate gearwheel. Here, the dog can be designed in a wide variety of different ways. For example, the dog can be designed as a peg manufactured in one piece with the intermediate gearwheel or be formed by a freely rotatable roller.
According to another advantageous development of the invention, the torsion spring takes up a particularly small amount of space if it is a spiral spring. If particularly high reliability against breakage of the spring is required, two identical spiral springs arranged one above the other can simply be used as the torsion spring.
According to another advantageous development of the invention, the torsion spring can be held reliably in its position if a guiding part resting laterally against the torsion spring is secured in the housing supporting the intermediate gearwheel.
According to another advantageous development of the invention, limiting the actuating range of the actuating shaft requires a particularly low level of expenditure in terms of construction if a stop plate which comes up against stops fixed relative to the housing in the minimum-load position and in the full-load position is secured in a rotationally fixed position on the actuating shaft. The stops can, of course, be designed to be adjustable to enable an idle setting or a full-load limit to be set.
Manufacturing the actuating part and the stop plate in one piece contributes to a further reduction in the manufacturing costs of the load adjustment apparatus according to the invention.